Method for removing toxic substances in water

ABSTRACT

Arsenic and TOC are removed from drinking water or wastewaters by use of finely-divided metallic iron in the presence of powered elemental sulfur or other sulfur compounds such as manganese sulfide, followed by an oxidation step. A premix may be produced for this process, by adding the iron, sulfur and oxidizing agent to water in a predetermined pH range. The iron and sulfur are mixed for a period of time dependent upon the temperature and pH of the water and the presence of complexing or sequestering minerals and organic acids in the water. An oxidizing agent is added to the mixture and agitating is continued. In a preferred embodiment the oxidizing agent is hydrogen peroxide. Water is decanted from the mixture after a sufficient reaction time, to produce a concentrated premix. This premix can be added to water intended for drinking or to industrial effluents containing toxic materials. Use of various gradations and mixtures of this sulfur-modified iron (SMI) premix have been successfully demonstrated to remove the following toxic substances from water: arsenic (arsenite and arsenate); disinfection byproducts and precursors; copper; chrome VI; sulfate; and chlorinated solvents including trichloroethene. Metals removed may be present in the untreated water in either the dissolved state or as a fine particulate. SMI has been fabricated using sulfur in the amount of up to 50% of the weight of the iron. SMI premix has been manufactured using a wetted but non-fluid mix at room temperature and at elevated temperature. SMI has been successfully demonstrated in pressure and gravity contact beds in both upflow and downflow modes. It has been prepared in uniformly-graded media similar in size and gradation to commercially-available filter media. Spent SMI can be recycled as a non-hazardous material as feed material to a steel production facility.

[0001] This is a continuation-in-part of application Ser. No.09/952,876, filed Sep. 14, 2001, now ______, which was acontinuation-in-part of application Ser. No. 09/624,713, filed Jul. 25,2000, which was a continuation of application Ser. No. 09/241,258, filedFeb. 1, 1999, U.S. Pat. No. 6,093,328, which was a continuation-in-partof application Ser. No. 08/742,652, filed Nov. 4, 1996, U.S. Pat. No.5,866,014, which was a division of application Ser. No. 08/352,383,filed Dec. 8, 1994, now U.S. Pat. No. 5,575,919.

BACKGROUND OF THE INVENTION

[0002] This invention is directed to a method and system which removesseveral regulated, toxic mineral and organic precursor substances fromdrinking water or wastewater by causing them to be absorbed and adsorbedonto sulfur-activated sponge iron particles, which may be referred to as“sulfur-modified iron”. Specifically, the method and system removes fromwater trace amounts of (1) dissolved, colloidal, and particulatearsenic, selenium, and lead; and (2) naturally-occurring organiccompounds (TOC, total organic carbon in the water), which, whenoxidized, form “disinfection byproducts”; and (3) other potentiallyharmful minerals.

[0003] The subject matter of this invention is related to some extent tothat of U.S. Pat. Nos. 4,940,549 and 5,200,082, which are directed toremoval of selenium from agricultural drain water and from refineryeffluents and other industrial waste waters. See also U.S. Pat. Nos.5,575,919, 5,866,014 and 6,093,328.

[0004] The process of the present invention is particularly concernedwith removal of arsenic and other toxic metals, and lowering the levelof TOC from drinking water, using some of the same steps which werefound efficacious in removal of selenium in the above referencedpatents.

[0005] Recent scientific investigations by the United StatesEnvironmental Protection Agency (EPA) and others have suggested thatarsenic in drinking water causes cancer in humans; that no quantity ofarsenic in drinking water is a safe quantity; that arsenic may not be anessential human nutrient as previously reported by science; and that thecancer risk from ingesting arsenic at the currently permitted level indrinking water may equal that caused by smoking cigarettes. The EPAcurrently is negotiating the content of the regulations for arsenic indrinking water and it projects that the new limitation will be between 2and 5 micrograms per liter (μg/L), most probably 2 μg/L.

[0006] Many existing water systems will have to treat to reduce theconcentration of arsenic. Three examples follow:

[0007] (a) The California State Water Project which hasnaturally-occurring arsenic in the amount of 2 to 6 μg/L provides waterfor several million families;

[0008] (b) The City of Hanford, Calif. gets its drinking water for morethan 20,000 people from ground water wells. Some of the wells havearsenic concentrations near the current limit of 50 μg/L;

[0009] (c) The Kern Water Bank is a project constructed to store waterin underground reservoirs in times of plenty for use when water is notavailable. Some of the Water Bank wells have naturally-occurringarsenic. In a few, the arsenic concentration approaches 200 μg/l.

[0010] Water providers have an immediate need for an economical, safemethod to remove arsenic from drinking water. Current methods, systems,and technologies have either proved to be uneconomical or ineffective tomeet the proposed 2 μg/L standard. The test for economical water serviceis as follows: Is the cost of water less than two percent of the grossincome of a family at the poverty level?

[0011] Existing technologies for removal of arsenic include thefollowing: (a) adsorption onto activated alumina within a fixed bedcontactor; (b) complexing arsenic with hydrous metallic floc, primarilyaluminum and iron hydroxides or oxyhydroxides, in conventional watertreatment plants; (c) sieving the metal from water by membranetechnologies such as reverse osmosis; and (d) electro-dynamic processessuch as electrodialysis. The present invention described below canexhibit a cost advantage of 5 to 15 times compared to these priormethods.

[0012] Also, since the middle 1970s, the EPA has warned that certainclasses of byproducts formed by oxidizing naturally-occurring organicacids during disinfection are potentially carcinogenic. These compoundsare regulated as “disinfection byproducts” (DBPs) to limit consumption.There are many DBP compounds of interest to EPA. Not all have been fullydescribed or investigated with respect to their potential effects onhuman health or the frequency of their occurrence in domestic watersystems. In addition, the epidemiological impact of DBPs is uncertain.Hence, there is a concerted effort of national scope to develop data onthe formation of DBPs and to better define their potential impact onhuman health.

[0013] The EPA is currently requiring more water systems to disinfecttheir water to limit the occurrence of waterborne disease, while at thesame time the EPA is seeking to reduce the impacts of DBPs on humanhealth; these can be conflicting purposes. Most water systems disinfecttheir water. Thus, many water systems will have to initiate or modifywater treatment systems to reduce DBPs to meet proposed trihalomethanelimitations which may range from 40 to 60 μg/L. Other DBPs, such ashaloacetic acids and several bromine compounds, will be subject tonumerical concentration limits. Conventional treatment systems forsurface water sources may meet many of the proposed standards ifinfluent precursors, i.e. TOCs, can be limited to 4 mg/L prior todisinfection with chlorine.

[0014] Thus, across the United States, water providers have an immediateneed for an economical, safe method to reduce the occurrence of DBPs indrinking water. Current methods, systems, and technologies have eitherproved to be uneconomical or ineffective to meet the proposed 40 to 60μg/L standard. The EPA has been proposing stringent limitations on theclass of DBPs known as trihalomethanes, cited above, since 1975. Waterproviders have often failed to meet the most basic requirement thattotal trihalomethanes be less than 100 μg/L.

[0015] As noted above, the primary strategy presently used to reduceDBPs is to control precursor chemicals early in the water treatmentprocess so that smaller quantities of disinfection byproducts formduring disinfection. Current alternative strategies include use ofnon-conventional disinfectants, treatment of the water to reduceformation of DBPs (in the presence of conventional disinfectants), andremoval of DBPs after formation. Existing technologies for reducing theconcentration of DBPs include the following: (a) adsorption of DBPs orprecursors onto granular activated carbon within a fixed bed contactoror adsorption onto powdered activated carbon during various stages ofthe treatment process; (b) complexing DBPs or precursors with hydrousmetallic floc, primarily aluminum and iron hydroxides, in conventionalwater treatment plants after adjusting the pH of influent water; (c)sieving the relatively-larger organic molecules from water by membranetechnologies such as ultrafiltration; and (d) electro-dynamic processessuch as electrodialysis.

[0016] It is an important object of the present invention to efficientlyand very economically remove arsenic, TOCs, and other contaminant metalsfrom drinking water. Procedures described can reduce cost of removingthese contaminants by a factor of five to fifteen, particularly ascompared to reverse osmosis or nanofiltration. It is a further object ofthe present invention to provide a method and system for removingarsenic, TOCs, and other contaminant metals which may be introduced intoexisting water treatment facilities. These and other objects of theinvention will be apparent to those skilled in the art from the detaileddescription of the invention contained herein and from the accompanyingdrawings.

SUMMARY OF THE INVENTION

[0017] The method of the present invention removes trace amounts ofcertain toxic substances in drinking water, specifically: (1) dissolved,colloidal, and particulate arsenic, selenium, and lead; and (2)naturally-occurring organic compounds (Total Organic Carbon or “TOC”)which, when oxidized, form disinfection byproducts; and (3) otherpotentially harmful minerals.

[0018] The invention utilizes a solid medium with a very high surfacearea finely-divided metallic elemental iron, or “sponge” iron. Themedium is manufactured by forming an oxidized surface in water in thepresence of finely-divided elemental sulfur or other sulfur-bearingcompounds such as manganese sulfide. The solid medium, which may becalled “sulfur-modified iron” and is sometimes thus referred to herein,is manufactured by mixing the constituents in water according topredetermined proportions. In one preferred embodiment of the presentinvention, these proportions may be approximately, by weight: 200 partsiron, 100 parts sulfur, and 1,000 parts water. The mixture is producedin water in a predetermined pH level, which for a preferred embodimentis in a range of pH between about 5.0 and 8.5. The normal processtemperatures can range from 34° Fahrenheit to near boiling. This blendis mixed for approximately two hours while the active agent forms.Mixing time depends upon the temperature of the mixture, pH of thewater, and the presence of complexing or sequestering minerals andorganic acids in the water. Lower temperature, higher pH and presence ofsuch complexing minerals generally will dictate longer mixing time. Inone preferred embodiment, an oxidizing agent is added to the mixtureafter the pH rises and stabilizes, and agitating is continued. In aspecific embodiment the oxidizing agent is hydrogen peroxide.

[0019] The solid sulfur-modified iron can be removed from the water inwhich it is manufactured and used to treat water. The treatment can beby batch or flow-through process. The sulfur-modified iron can beremoved from the process stream by gravity separation processes, bycentrifugal force, or by magnetic separation processes.

[0020] In the batch treatment process, untreated water and thecomponents of sulfur-modified iron or pre-formed sulfur-modified ironare mixed vigorously for a variable period of time. The duration ofmixing can be for as little as 5 minutes or as long as two hoursdepending upon the state of completeness of the sulfur-modified iron andthe physical constants of the water to be treated. The mixing can beprovided by airlift pumps, hydraulic mixing, action of a fluidized bed,mechanical mixers, or by other measures. Note that the batch treatmentprocess can employ a pre-mix of sulfur-modified iron, or the iron andsulfur can be separately mixed into the untreated water. Parameters suchas mix time will vary depending on which procedure is used.

[0021] In the flow-through process, the preferred process, thesulfur-modified iron is pre-prepared and resides in an upflow, fluidizedbed reactor or other fully-mixed reactor vessel for an appropriateperiod of time. The sulfur-modified iron remains in the reactor byvirtue of its relatively high specific gravity, 2.6±, while theuntreated water flows past in turbulent mixing. Necessary resident timein the reactor is approximately 5 minutes, depending upon severalprocess variables. Alternately, the process can take place in a pebbleflocculator or contact clarifier apparatus in which the sulfur-modifiediron is affixed to the surface of the treatment medium within the vesselor recirculated within the reaction zone of the process. Anotheralternative is to introduce the sulfur-modified iron into the centerwell of a rapidly mixed contact clarifier in a water or wastewatertreatment plant.

[0022] It is believed that the sulfur-modified iron will become depletedin its capacity to absorb and absorb toxic substances from water afterabout 100,000 pore volumes, more or less, have been treated. At thattime, it may be replenished by removing the toxic substances. It may bethat the sulfur-modified iron can be replenished and reused by washingit with an appropriately selected basic or acidic liquid. The choice ofthe replenishing fluid will be dictated by the economics of the specificinstallation in which it is used. The characteristics of the untreatedwater may permit resource recovery from the regeneration fluids.Removal, regeneration, and replacement can be a continuous flow orperiodic batch process.

[0023] In practice, the contact vessel used for treatment can be eithera mixed container or a gravity filter-like contactor (upflow ordownflow) or a fluidized bed contactor. Contact times for effectivetreatment of a variety of contaminants have varied from as little 3minutes to as long as 30 minutes.

[0024] Use of various gradations and mixtures of sulfur-modified iron(SMI) have been successfully demonstrated to remove the following toxicsubstances from water: arsenic (arsenite and arsenate); disinfectionbyproducts and precursors; copper; chrome VI; sulfate; and chlorinatedsolvents including trichloroethene. Metals removed may be present in theuntreated water in either the dissolved state or as a fine particulate.See to the tables below, entitled “Summary of SMI Laboratory Testing”and “Laboratory Development Studies of SMI.” In most cases, tests wereconducted using fixed bed reactors. In some cases, the beds in thesereactors were periodically disturbed by counter-current flow to preventagglomeration of the media.

[0025] SMI has been fabricated using sulfur in the amount of up to 50%of the weight of the iron and as little as 3%. The full effect of sulfurto iron ratio has not been fully explored; however, the SMI mix iseffective against a range of contaminants regardless of this ratio. SMIpremix has been manufactured using a wetted but non-fluid mix at roomtemperature and at elevated temperature.

[0026] SMI has been successfully demonstrated in pressure and gravitycontact beds in both upflow and downflow modes. SMI has been prepared inuniformly-graded media similar in size and gradation tocommercially-available filter media.

[0027] Spent SMI can be recycled as a non-hazardous material as feedmaterial to a steel production facility. For such use the spent SMI mustnot contain sufficient toxic material to be classified as hazardous forpurposes of transportation of waste materials, and the steel facilitymust have off-gas scrubbing equipment installed to handle the toxicmaterials released when spent SMI is incorporated into the metalsproduced.

DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a schematic flow chart of the use of a preparation ofsulfur-modified iron according to a batch process.

[0029]FIG. 2 is a schematic flow chart of a prior-art water treatmentprocess/plan indicating the addition of a flow-through treatment reactoraccording to the present invention. In each of FIGS. 1 and 2 the contactvessel can be understood to be either a mixed container or a gravityfilter-like contactor (upflow or downflow) or a fluidized bed contactor.Further, mixing in a fully-mixed reactor is unnecessary to obtain fullbenefit of the SMI treatment for removal of contaminants.

[0030]FIG. 3 illustrates a reactor according to an embodiment of thepresent invention for producing sulfur-modified iron.

[0031]FIG. 4 is a schematic elevation view showing a filter-likecontactor as a reaction vessel.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0032] As specified above, the method of the present invention removedtrace amounts of certain toxic substances or precursors to toxicsubstances in drinking water. This process depends upon the creation oruse of a solid medium with a very high surface area produced fromfinely-divided metallic elemental iron called “sulfur-modified iron”herein, as explained above. The medium is generated by forming anoxidized iron surface in water in the presence of finely-definedelemental sulfur or other sulfur-bearing compounds such as manganesesulfide.

[0033] Accordingly, FIG. 3 illustrates a preferred method for thecreation of sulfur-modified iron. A reaction vessel 10 is filled withwater at 12. Next, a fluid is introduced at 14 to bring the mixture to apredetermined pH level, which for one preferred embodiment is in a rangeof pH between 5.0 and 8.5, more broadly, about 3.5 to about 10. Inaddition, heat may be introduced or recovered by heat exchanger 30 asappropriate to bring the water into an acceptable temperature range.Normal process temperatures range from 34° F. to near boiling. As notedbelow, some elevation of temperature above standard (room) temperaturehas been found effective in facilitating a lesser reaction time.

[0034] A modified method is described below following the examples, bywhich minimal water is used and the exothermic nature of the reaction isused to speed the reaction and substantially to dry the mixture atcompletion of the reaction.

[0035] Sulfur-modified iron may be manufactured by pre-mixing theconstituents in water according to predetermined proportions, asexplained above. First, “sponge iron” is added at 16 and agitated by amixer 20 for a period of time, for example one hour in one preferredembodiment. Sponge iron with particle sizes of 325 mesh or slightlylarger are preferred. Next, sulfur is added at 18 and the mixture isagain agitated by mixer 20, for 45 minutes in the embodiment describedimmediately above. In addition to elemental sulfur, it is believed thatsulfur compounds such as manganese sulfide may be substituted.

[0036] In a preferred embodiment of the present invention, in preparinga pre-mix sulfur-modified iron, proportions of the reactants areapproximately, by weight: 200 parts iron, 100 parts sulfur, and 1,000parts water. This blend is mixed while the active agent forms. Mixingtime depends upon the temperature of the mixture, pH of the water, andthe presence of complexing or sequestering minerals and organic acids inthe water, as noted above.

[0037] Next, in the preferred embodiment described, an oxidant may beadded at 22, after the pH of the sulfur-iron-water suspensionstabilizes. In the preferred embodiment discussed above, one part ofhydrogen peroxide is introduced and the mixture is agitated by the mixer20 for about 15 minutes.

[0038] Finally, the resulting solid sulfur-modified iron can be largelyremoved from the water in which it is manufactured, and can be used totreat water.

[0039] The preferred usage of sulfur-modified iron is in a flow-throughprocess in the water treatment system as described above. In thisflow-through process, the sulfur-modified iron is pre-prepared andresides in an upflow reactor or other fully-mixed reactor vessel. Asdescribed above, in this system the sulfur-modified iron is retained inthe reactor by gravity while at the same time fully-mixed contact takesplace as the water flows upward. The resulting mixture of toxicsubstances and sulfur-modified iron is separated and removed from thecleaned water by gravity, centrifugal force, or magnetic separation. Thesulfur-modified iron may be recycled by regeneration, using anappropriate acidic or basic rinse solution.

[0040] Such a reactor may be introduced into an existing water treatmentplant as shown in FIG. 2. First, a valve 122 is inserted betweenchemical feed vault 120 and influent pumps 140. New piping 124 and 126are introduced to convey water into and out of, respectively, the newreactor 130. Sulfur-modified iron can be introduced from infeed 132 andremoved by outfeed 134.

[0041] The sulfur-modified iron will ordinarily remain in the reactor130 by virtue of its relatively high specific gravity, 2.6±, while theuntreated water flows past in turbulent mixing. Necessary residence timein the reactor 130 is approximately 5 minutes, depending upon severalprocess variables.

[0042] Alternately, the process can take place in a pebble flocculatoror contact clarifier apparatus in which the sulfur-modified iron isaffixed to the surface of the treatment medium within the vessel orrecirculated within the reaction zone of the process. Anotheralternative is to introduce the sulfur-modified iron into the centerwell of a rapidly mixed contact clarifier in a water or wastewatertreatment plant.

[0043] The sulfur-modified iron will become depleted in its capacity toadsorb and absorb toxic substances from water after a number of porevolumes (believed to be about 100,000 pore volumes) have been treated.At that time, as discussed above, it can be replenished by removing thetoxic substances. It is believed that the sulfur-modified iron can bereplenished and reused by washing it with selected acidic or basicliquids, such as a caustic soda, to pull the organic compounds off thesurface of the iron. The choice of the replenishing fluid will bedictated by the economics of the specific installation in which it isused. The characteristics of the untreated water may permit resourcerecovery from the regeneration fluids. Removal, regeneration, andreplacement can be a continuous flow or periodic batch process.

[0044] An alternative method of producing sulfur-modified iron and oftreating the influent water in the same process is illustrated inFIG. 1. In this batch treatment process, untreated water and either ironand sulfur or pre-formed sulfur-modified iron are mixed vigorously for avariable period of time. The duration of mixing can be for as little as5 minutes or as long as two hours depending upon the state ofcompleteness of the formation of the sulfur-modified iron and thephysical constants of the water to be treated, including temperature andpH. The mixing can be provided by airlift pumps, mechanical mixers, orby other measures.

[0045] Water enters and is stored in a surge tank at 212, and a fluid isintroduced at 214 to bring the mixture to a predetermined pH level,which for the preferred embodiment is in a range in pH between 3.5 and8.5. An acid pH range generally causes the process to work moreefficiently. However, economic considerations dictate that acidificationshould be avoided if practicable. Drinking water often is in a range ofpH 7.5 to 9.5 (to avoid corrosion of pipes). An efficient range of pH is5.0 to 8.5, but slightly higher pH can be acceptable, depending oncontent of the water. In addition, heat may be introduced as appropriateto bring the water into an acceptable range. The normal processtemperatures range from 34° F. to near boiling, but temperatures aboveroom temperature tend to produce faster reaction time. Of course, it ismore economical not to heat the water if this can be avoided withinpractical time constraints.

[0046] Next, at first stage 218, sponge iron at 222 is added andagitated by a mixer. Either sponge iron or partially preparedsulfur-modified iron may be used. Next, if iron alone has been added,sulfur is added at 220 and the mixture is again agitated for anadditional period of time. As mentioned above, it is believed thatsulfur compounds such as manganese sulfide may be substituted.

[0047] Next, an oxidant at 224 is added at to the mixture at the secondstage 226, after the pH of the sulfur-iron-water suspension stabilizes.Again, in the preferred embodiment discussed above, one part of hydrogenperoxide is introduced (relative to 200 parts iron and 100 parts sulfurby weight) and the mixture is agitated.

[0048] Finally, the reacted solid sulfur-modified iron can be removedfrom the water by magnetic separation, gravity or centrifuge, asindicated at 228. The treated water 234 may then be subjected to furthertreatment as conventional.

[0049] In addition to the form described above, the sulfur-modified ironmay be affixed to a substrate solid material such as silica, alumina,ceramic, or other materials. This approach has the disadvantage that theuse of the substrate diminishes the effectiveness of the sulfur-modifiediron by diminishing its surface area, and the advantage of being easierto suspend in the water than particulate iron. Another potentialadvantage is in allowing a combination with other catalysts. There areapplication techniques wherein the less-mobile substrate (less easilysuspended) is more practical and desirable, such as in a point-of-usewater filter.

[0050] Water treatment science has examined many of the reactionsassociated with removal of toxic substances from water including (a)chemical and biological oxidation and reduction phenomenon; (b)formation of metallic and non-metallic hydroxides or oxyhydroxides inconventional water treatment processes; (c) chemical precipitationprocesses; (d) molecular sieve process such as reverse osmosis andultra-filtration; and (e) electromotive-force process such aselectrodialysis. The family of sulfur-modified iron processes developedaccording to the invention and described herein has not been describedat the atomic level by water treatment researchers, nor have the processperformance characteristics been defined independently of the workperformed pursuant to this invention. Perhaps the closest relatedprocesses are the Fenton-Reagent Process and the ferric sulfidecoagulation processes which do not use solid, particulate chemicals, butuse liquid.

[0051] Recent experiments in corrosion science have produced photographswith atomic-level resolution of the formation of rust on iron particlesin water. This work, reported by Roger C. Newman in “Science”, vol.263,1708 & 1709, states “the passive oxide film on iron is none of the knownhydroxides or oxyhydroxides”. He further reports that “the iron in thefilm is surrounded by six oxygen atoms in a distorted octahedralarrangement, and that these octahedra share edges and faces, perhapsforming sheets or chains”. It is believed, according to this invention,that the oxide film that forms on the porous, elemental iron in thepresence of sulfur causes one or more of the oxygen atoms to be replacedwith sulfur, causing the formation of the unique surface-activetreatment agent: sulfur-modified iron. The use of this solid,particulate material rather than liquid reagents provides for moreeconomical and effective contaminant removal than processes usedpreviously.

[0052] By the processes described herein, treatment with sulfur-modifiediron has removed precursors of DBPs, analyzed as Total Organic Carbon,from natural water sources to a concentration of 4 mg/L or less. TotalOrganic Carbon concentration in the untreated water of test samplesvaried from 6 to 20 mg/L. In the case of paper mill acid ditch effluent,COD was reduced from 3080 to 2100 with only 15 minutes reaction time.

[0053] Sulfur-modified iron also has consistently removed arsenic fromnatural water sources to less than 5 μg/L (the practical quantitativelimit of test equipment used for analyses.) Arsenic concentration in theuntreated water varied from 34 to 170 μg/L.

[0054] Several examples of the results of the procedure on arsenicremoval are presented in Examples 1 through 4, 6 and 10 below. Examplesdemonstrating the results of the procedure on TOC removal are presentedin Examples 5 through 9 and 11 below.

[0055] In the examples reported below, the quantity of particulate ironemployed, as compared to the amount by weight of arsenic contaminatingthe water, often is in a ratio of about 1000:1, sometimes less,sometimes greater. The amounts of powdered iron ranged in most casesfrom about 0.15 gram to 0.5 gram. However, it is believed that theamount of iron could be reduced down to about 0.01 g/L, or even 0.005g/L, for effective removal of most of the contaminating arsenic in thesample quantities disclosed. The amount of sulfur is generallymaintained at about one-half by weight the amount of iron, which it isbelieved will hold true with the smaller quantities of iron projectedabove.

[0056] The examples set forth below have all employed granular, powderediron or “sponge iron”, and from the experience of testing it is believedthat an effective range of iron particle sizes about −20 to about −400mesh. However, iron in any particle size will have some efficacy, incombination with the steps and other reagents described, in removingarsenic, TOC and AOX from water. One procedure for removing thesecontaminants, not described in the examples below, is to form a bed ofsulfur-modified iron particles, but with a larger particle size, up toabout ¼ inch. This bed, arranged in the manner of a granular filter bedor contact bed, provides a stable medium through which the contaminatedwater is directed, by gravity or pumping. This arrangement can serveefficiently in a water treatment system.

EXAMPLE 1 Arsenic in Well Water

[0057] A sample was obtained from the Kern County Water Agency as a partof the normal sampling run of the wells in the Kern Water Bank. The wellis owned by the California Department of Water Resources. This well,designated 32N2, has naturally-occurring arsenic. The sample was storedat approximately 34° F. In the water sampled during this run, thearsenic concentration was 170 μg/L. Other than the elevatedconcentration of arsenic, this well water is typical of well water usedthroughout the California Central Valley for domestic water service.

[0058] This sample was treated for removal of arsenic by batch treatmentby the method and system of this invention. Starting temperature of the1,000 mL sample was 60° F. and pH was 8.8. The sample was acidified topH 4.3 with 3 mL, 1N sulfuric acid. To the acidified water sample wasadded 0.3 grams of finely-divided sponge iron and 0.1 gram of finelydivided elemental sulfur (no pre-mix of sulfur-modified iron wasprepared). The previously-clear mixture turned cloudy. Afterapproximately 1 hour and 20 minutes, one drop of hydrogen peroxide wasadded to the mixture; pH was 6.1 before the H₂O₂ and 5.5 after. Themixture was stirred rapidly for total time of 1 hour and 53 minutesafter adding the iron at which time a sample of the decanted mixture wassent to a certified water quality laboratory for analysis for arsenic.Arsenic concentration reported was less than the practical quantitationlimit of 5 μg/L.

EXAMPLE 1—Mar. 28, 1994

[0059] TIME TEMP As (min) ACTIVITY pH ° F. LAB NOTES (μg/L) −30Refrigerated Kern Water Bank well 8.8 34 Clear, stirring slowly 170water in unopened 1 L sample bottle. Well 32N2 −15 Add 3 mL 1 N H₂SO₄4.3 60 Clear, stirring slowly −10 Add 0.3 g Fe, Grade B 4.1 Clear,stirring slowly 0 Add 0.1 g S, dry, powdered Cloudy, stirring slowly 0Increase stirring to rapid Cloudy, rapid +20 6.1 Cloudy, rapid +20 Add 1drop 3% H₂O₂ 5.5 Cloudy, rapid +112 Decant and sample. Laboratory 6.4Cloudy (before ND filter. filtration)

EXAMPLE 2 Arsenic in Well Water

[0060] Example 2 uses the same sample water source and treatmentdynamics as Example 1 and is a confirmation of the methods of Example 1.The reagent quantities and procedures varied lightly.

EXAMPLE 2—Apr. 4, 1994

[0061] TIME TEMP As (min) ACTIVITY pH ° F. LAB NOTES (μg/L) −30Refrigerated Kern Water Bank well 9.3 34 Clear, stirring 170 water inunopened 1 L sample rapidly bottle. Well 32N2 −10 Add 3 mL 1N H₂SO₄ 3.560 Clear, stirring rapidly −5 Add 0.2 g Fe, MH-100 3.4 Clear, stirring(slightly coarser than Grade B) rapidly 0 Add 0.1 g S, dry, powdered 3.4Cloudy, stirring slowly +15 5.6 Cloudy, rapid stirring +15 Add 1 drop 3%H₂O₂ 4.5 Cloudy, rapid +161 Decant, filter, & sample. 5.8 Cloudy(reddish) ND

EXAMPLE 3 Arsenic in Well Water

[0062] Example 3 uses the same sample water source and treatmentdynamics as Examples 1 and 2. It is a confirmation of the methods ofExamples 1 and 2, with slightly different reagent quantities andprocedures, including acid and iron quantities. Note that initial pH inExamples 1-3 is 8.8 to 9.3, with essentially complete arsenic removal.

EXAMPLE 3—Apr. 13, 1994

[0063] TIME TEMP As (min) ACTIVITY pH ° F. LAB NOTES (μg/L) −30Refrigerated Kern Water Bank well 9.0 34 Clear, stirring 170 water inunopened 1 L sample rapidly bottle. Well 32N2 −10 Add 1.5 mL 1N H₂SO₄6.4 60 Clear, stirring rapidly 0 Add 0.15 g Fe, MH-100 6.0 Clear,stirring rapidly 0 Add 0.1 g S, dry, powdered 6.0 Cloudy, stirringslowly +25 6.1 Cloudy, rapid +15 Add 1 drop 3% H₂O₂ 5.7 Cloudy, rapid+170 Decant, filter, & sample. 7.8 Cloudy ND

EXAMPLE 4 Arsenic in Well Water

[0064] Example 4 uses the same sample water source and treatmentdynamics as Examples 1, 2, and 3, except that sulfur is not added(except as present in sulfuric acid). It is a confirmation of themethods of the previous examples, but indicating that arsenic removal isnot as complete without addition of sulfur.

EXAMPLE 4—Apr. 17, 1994

[0065] TIME TEMP As (min) ACTIVITY pH ° F. LAB NOTES (μg/L) −30Refrigerated Kern Water Bank well 9.4 34 Clear, stirring 170 water inunopened 1 L sample rapidly (until bottle. Well 32N2 decant) −10 Add 3ml 1N H₂SO₄ 3.5 60 0 Add 0.2 g Fe, MH-100 3.0 +15 Add 1 drop 3% H₂O₂ 3.5+185 Decant, filter, & sample 5.3 6

EXAMPLE 5 TOC in Surface Water

[0066] A water sample, 2½ gallons, was taken from Rock Slough Bridge(Br.#RSB5/28), Contra Costa County, California at the same point thatContra Costa County Water District (California) samples its source waterfor its water treatment plant. The sampling time was coordinated withthe District sample run. The purpose of this test and sample is todemonstrate removal of total organic carbon from surface water.

[0067] The treatment is essentially the same as described in Example 1.The major difference is that the treated water was rich in naturalorganic chemicals which tend to bind the iron and reduce its treatmenteffectiveness. It should be kept in mind that the TOC content in sampleswill decrease somewhat with time following taking of the sample, withoutany treatment, because some of the content of TOC is volatile. EXAMPLE 528 APR. 1994 TIME TEMP TOC (min) ACTIVITY pH ° F. LAB NOTES mg/L −30 800mL refrigerated Rock Slough 8.1 34 Blend, stirring rapidly 5 waterblended with 200 mL Kern Water Bank well water −10 Add 2.5 mL 1N H₂SO₄5.5 60 Blend, stirring rapidly −5 Add 0.2 g Fe, Grade B 5.5 Blend,stirring rapidly 0 Add 0.1 g S, dry, powdered 5.5 +15 5.9 +15 Add 2drops 3% H₂O₂ 5.6 Continued rapid stirring +50 30 mL sample filteredwith 4 Whatman 42

EXAMPLE 6 TOC & Arsenic in Surface Water

[0068] This example used the same sample as Example 5, but “spiked” witharsenic by mixing 800 mL of surface water with 200 mL of the water fromthe Kern Water Bank well 32N2, described in Example 1.

EXAMPLE 6—Apr. 29, 1994

[0069] TIME TEMP TOC As (min) ACTIVITY pH ° F. LAB NOTES mg/L μg/L −20800 mL refrigerated Rock Slough 8.2 34 Blend, rapid 7.0 34 water blendedwith 200 mL Kern stirring Water Bank well water −5 Add 2 mL 1N H₂SO₄ 4.80 Add 0.2 g Fe, Grade B 0 Add 0.1 g S, dry, powdered 4.6 +18 5.5 +18 Add3 drops 3% H₂O₂ 5.0 +80 100 mL sample filtered with Continued rapid 5.0Whatman 42 stirring until filtration +80 50 mL sample, unfiltered 26

EXAMPLE 7 TOC in Surface Water

[0070] The same Rock Slough surface water, a source of drinking waterbefore treatment, was treated alone, without addition ofarsenic-containing water. Tests were conducted using the method of theinvention, in order to reduce the concentration of TOC in the water.

EXAMPLE 7—May 7, 1994

[0071] TIME TEMP LAB TOC (min) ACTIVITY pH ° F. NOTES mg/L −20 1,000 mLrefrigerated Rock 8.1 34 Clear 7.0 Slough water −5 Add 2 mL 1N H₂SO₄ 4.80 Add 0.2 g Fe, Grade B 0 Add 0.1 g S, dry, powdered 4.6 +18 5.5 +18 Add3 drops 3% H₂O₂ 5.0 +80 100 mL sample Continued 5.0 filtered with rapidWhatman 42 stirring until filtration +80 50 mL sample, unfiltered

EXAMPLE 8 TOC in Surface Water

[0072] The surface water sample was taken from the same point on RockSlough as the previous examples three hours before this test. A shortertest period was used to develop data on the maturation of the activeagent. This experiment was conducted to determine the influence of pHadjustment on the effectiveness of the active agent. The processappeared to remain effective at a higher pH, all other variablesremaining the same, except the oxidizing agent, which was sodiumhypochlorite in this test. This test also shows that the process worksin the presence of alum, which is often used in municipal treatmentplants.

EXAMPLE 8—May 10, 1994

[0073] TIME TEMP TOC (min) ACTIVITY pH ° F. LAB NOTES mg/L −180 1,000 mLRock 8.2 4.0 Slough water 0 Add 0.2 g Fe, Grade B Rapid stirring 0 Add0.1 g S, 7.6 Rapid stirring dry, powdered +10 Add 9 drops 8.1 Rapidstirring 5.35% sodium hypochlorite solution +15 Add 3 drops 8.3 Slowstirring 50% aluminum sulfate solution +18 7.3 Slow stirring +30 100 mLsample, 7.1 3.0 filtered with Whatman 934-AH

EXAMPLE 9 TOC in Surface Water

[0074] The surface water sample was taken from the same point on RockSlough as the previous examples one hour and 40 minutes before thistest. This sample was taken to investigate the performance of the activeagent during severe deteriorations in water quality.

EXAMPLE 9—Jun. 1, 1994

[0075] TIME TEMP TOC (min) ACTIVITY pH ° F. LAB NOTES mg/L −115 1,000 mLRock 3.8 12 Slough water −5 Add 5 mL 1N H₂SO₄ 3.4 60 Rapid stirring 0Add 0.3 g Fe, Grade B 60 Rapid stirring 0 Add 0.2 g S, dry, 60 Rapidstirring powdered +25 Add 4 drops 3% H₂O₂ 6.1 60 Rapid stirring +135 100mL sample 6.2 60 No stirring 6.0 filtered with Whatman 934-AH +175 100mL sample, 7.3 Clear 5.0 filtered with supernate. Whatman 934-AH Gasevolving from sludge.

EXAMPLE 10 Arsenic in Well Water, Treated with Sulfur-modified IronPre-mix

[0076] In this example, a pre-mix was prepared of reagents in distilledwater, prior to introduction into the well water to be treated forarsenic. This shows that reaction can be achieved in the pre-mix,sufficient to form a reactive, concentrated reagent mix for additiondirectly to the water to be treated, without need for direct applicationof the individual non-reacted reagents (iron, sulfur, oxidizing agent)to the well water. The advantage is that a much smaller reaction vesseland much less mixing energy is used to achieve treatment as comparedwith not using premix.

[0077] To one liter of distilled water, powdered iron (sponge iron),elemental sulfur and a 3% hydrogen peroxide solution were added. Thequantities were as follows: Grade B iron, 0.5 g; elemental sulfur, 0.2g; hydrogen peroxide, 0.5 mL. No acid was included. These reagents werestirred in the one liter of water for one hour. After stirring, 980 mLof water were decanted off the settled mixture, leaving 20 mL ofconcentrated reagent mix, i.e., sulfur-modified iron. The concentratedreagent was then added to one liter of Kern County well water having anarsenic content of 40 μg/L. The procedure is shown in the followingtable:

EXAMPLE 10—Sep. 10, 1994

[0078] TIME TEMP As (min) ACTIVITY pH ° F. LAB NOTES μg/L 1 L KernCounty 7.3 60 40 well water, 15C1 0 Add 20 mL 60 Rapid stirringsulfur-modified iron (continuous) pre-mix +10 50% removal 20 +20 60%removal 16 residue brown (continuous)

[0079] This example shows that an effective mix can be prepared and willaccomplish the removal of arsenic from drinking water in substantiallythe same manner as with the above examples which involved separateaddition of each of the individual reagents. The example alsodemonstrates that a great deal of arsenic removal is accomplished, usingthe pre-mix as above, in a very early phase of the process. Over 50%removal was effected in the first ten minutes; 60% in the first twentyminutes. It is projected that removal would be complete to the point ofless than 5 μg remaining, if the reaction were taken to approximately 45minutes. Also, it is believed the reaction would be accelerated if theperoxide were added to the entire batch of well water, at a timesubsequent to the addition of iron and sulfur. It is also believed thatthe process could be accelerated if acid were added to reduce the pH toan acid range.

EXAMPLE 11 Removal of TOC (AOX) from Paper Mill Acid Ditch Liquor

[0080] In this test, procedures similar to the above were applied toeffluent “acid ditch” liquor of a James River Corporation paper mill.Example 11 involved preparation of a premix of iron, sulfur and peroxidein distilled water, with the premix then being introduced to the acidditch sample. The premix was prepared using a laboratory chemical mixer.Table 11 below reports the results of Example 11, with variouscomponents of the acid ditch liquor quantified both before and aftertreatment by the process of Example 11.

EXAMPLE 11—Jul. 31, 1994

[0081] TIME TEMP COD AOX (min) ACTIVITY pH ° F. LAB NOTES mg/L mg/L −901,000 mL distilled water, for 7.0 60 premix −85 Add 0.4 g Fe, Grade B 60Rapid stirring −85 Add 0.2 g S, powdered Rapid stirring −70 Add 6 drops3% H₂O₂ 60 Rapid stirring −15 Decant off 950 mL H₂O, 60 leaving 50 mLpremix 0 1 L James River liquor. Add 60 Rapid stirring 3080 80.0 premixof sulfur-modified iron +15 100 mL sample, filtered with 60 2100 58.9Whatman 934-AH

[0082] TABLE 11 Acid Ditch - Acid Ditch - Analyte Untreated Treated BOD₆(ppm) 561 403 COD (ppm) 3080 2100 pH 6.1 5.1 TSS (ppm) 403 25 Color(NCASI color, units) 3170 4240 Chlorinated Phenolics (ppb): 2,4,5Trichlorophenol ND(2.5) ND 2,3,6 Trichlorophenol 69 57 2,3,4,6Tetrachlorophenol ND(2.5) ND Pentachlorophenol ND(5) ND 3,4,5Trichloroguaiacol 24 ND 3,4,6 Trichloroguaiacol 7.3 ND 4,5,6Trichloroguaiacol 18 ND Tetrachloroguaiacol 8.8 ND 3,4,5Trichlorocatechol 110 88 3,4,6 Trichlorocatechol ND(5) NDTetrachlorocatechol 15 ND Trichlorosyringol ND(2.5) ND AOX (ppb) 80,00058,900

[0083] As noted, the results reported in table 11 were taken from sampleJR2.2, after only 15 minutes of reaction time of the sulfur modifiediron premix with the James River acid ditch liquor sample. Table 11shows dramatic results for this short reaction time. COD alone wasreduced from 3080 mg per liter to 2100 mg per liter. AOX (purgeableorganic halides), was reduced from 80,000 to 58,900 μ/L. The trend ofthe above examples, and additional experience with the method of theinvention, have indicated that improved results will be obtained if theoxidizing agent, e.g. hydrogen peroxide, is added later in the reaction,i.e. not as part of the prepared premix but after a certain reactiontime of the iron and sulfur with the liquor.

[0084] The disclosed method and system remove a range of toxicsubstances economically and effectively in either large, municipal-sizeddrinking water treatment plants or smaller single-home or industrialunits. The method and system can be applied as a stand-alone treatmentor in conjunction with other processes. The original source of theuntreated domestic water or wastewater can be ground water, surfacewater or certain industrial effluents.

EXAMPLE 12 Arsenic in Mining Water

[0085] A 55-gallon drum of water containing approximately 1 mg/L ofarsenic was obtained from the Wharf Mine, a gold mine in Lead, S.Dak. Itwas determined that the arsenic was present as As⁵⁺ (arsenate), so anoxidizing agent was not added in the experiment. The purpose of thisexperiment was to determine the removal efficiencies of arsenic withrespect to iron addition over a 22-hour period, and therefore todetermine an adsorption isotherm at pH 8. Grade B iron and elementalsulfur were added at a 2:1 Fe:S ratio with no pre-wetting of iron orsulfur. The Fe:As ratios were 633:1, 316:1, 158:1, 79:1 and 40:1.

[0086] Adsorption isotherms generated from bench-scale tests predict theamount of contaminant removed (in this case, arsenic) for a given amountof adsorbate (in this case, iron and sulfur). Adsorption isotherm testsare “static” tests in that water does not continuously flow over theadsorbate. The removal rate predicted from an isotherm is thetheoretical maximum amount adsorbed at equilibrium conditions, althoughbetter results are occasionally obtained in continuous-flow conditions.

[0087] Five jars in a mixing unit were filled with two liters each ofcontaminated water with an initial pH of 8.87. Each jar was acidified topH 8 with several drops of 12 N HCl. Varying quantities of Grade B ironand elemental sulfur were added to each jar to obtain the aforementionedratios. The jars were stirred rapidly in a mixing unit at 300 rpm. After22 hours, the water from each jar was filtered into 250-ml samplebottles and sent to a certified water quality laboratory for analysis ofdissolved arsenic.

EXAMPLE 12—Dec. 22, 1997

[0088] TIME TEMP As (min) ACTIVITY pH (° F.) LAB NOTES (mg/L) −25 Add 2L of Wharf water to 5 jars. 8.87 68 Yellow tinged 0.632 water −15 Addseveral drops 12 N HCl to each jar. 8.00 0 Increase speed of mixing unitto 300 rpm. 0 First jar: add 0.8 g Fe, Grade B, dry and 8.24 Yellowtinged 0.4 g S, dry, powdered. water 0 Second jar: add 0.4 g Fe, GradeB, dry 8.22 Yellow tinged and 0.2 g S, dry, powdered. water 0 Third jar:add 0.2 g Fe, Grade B, dry and 8.19 Yellow tinged 0.1 g S, dry,powdered. water 0 Fourth jar: add 0.1 g Fe, Grade B, dry and 8.20 Yellowtinged 0.05 g S, dry, powdered. water 0 Fifth jar: add 0.05 g Fe, GradeB, dry and 8.16 Yellow tinged 0.025 g S, dry, powdered. water 10 Addseveral drops 12 N HCl to each jar. 8.00 1320 Filter samples from eachjar. 8.60 Yellow tinged water DISSOLVED ARSENIC JAR Fe:As RATIOCONCENTRATION (mg/L) 1 633:1 ND 2 316:1 ND 3 158:1 0.005 4  79:1 0.028 5 40:1 0.060

[0089] The results demonstrate that in all five sub-examples, there isremoval of the arsenic from the water. While low ratios of iron toarsenic appear to be less effective than with higher ratios, arseniclevels are still substantially reduced. For example, in the case of a40:1 ratio of iron to arsenic, the arsenic level in the water wasreduced from approximately 1 mg/L to 0.060 mg/L. The examples show thatremoval is still very effective at less than 100:1 iron to arsenic.

[0090] Furthermore, this example demonstrates that in the case wherearsenate is present, the effective results may be obtained withoutintroduction of an oxidizing step.

EXAMPLE 13 Arsenic in Mining Water

[0091] Example 13 used the same sample water source and treatmentdynamics as Example 12 except the sample water was acidified to pH 7with 12 N HCl and the Fe:As ratios were adjusted to 225:1, 170:1, 112:1,56:1, 28:1 and 11:1. The Grade B iron and elemental sulfur were notpre-wetted, and an oxidizing agent was not added. The initial arsenicconcentration was lower than in Example 12 because some of the arsenichad precipitated while being stored in the drum. The pH in each jarincreased from 7.0 to approximately 7.9 during the experiment.

EXAMPLE 13—Jan. 20, 1998

[0092] TIME TEMP As (min) ACTIVITY pH (° F.) LAB NOTES (mg/L) −25 Add 2L of Wharf water to 5 jars. 9.02 68 Yellow tinged 0.112 water −15 Addseveral drops 12 N HCl to each 7.00 jar. 0 Increase speed of mixing unitto 300 rpm. 0 First jar: add 0.05 g Fe, Grade B, dry 7.92 Yellow tingedand 0.025 g S, dry, powdered. water 0 Second jar: add 0.038 g Fe, GradeB, 7.91 Yellow tinged dry and 0.019 g S, dry, powdered. water 0 Thirdjar: add 0.025 g Fe, Grade B, dry 7.85 Yellow tinged and 0.0126 g S,dry, powdered. water 0 Fourth jar: add 0.0126 g Fe, Grade B, 7.92 Yellowtinged dry and 0.0063 g S, dry, powdered. water 0 Fifth jar: add 0.0063g Fe, Grade B, dry 7.90 Yellow tinged and 0.0032 g S, dry, powdered.water 0 Sixth jar: add 0.0025 g Fe, Grade B, 7.89 Yellow tinged dry and0.0013 g S, dry, powdered. water 10 Add several drops 12 N HCl to each7.00 jar. 1320 Filter samples from each jar. 7.50 Yellow tinged water,Fe oxidizing DISSOLVED ARSENIC JAR Fe:As RATIO CONCENTRATION (mg/L) 1225:1 ND 2 170:1 ND 3 112:1 0.008 4  56:1 0.012 5  28:1 0.010 6  11:10.050

[0093] As in Example 12, this example demonstrates the effectiveness ofthe process with lower iron to arsenic ratios, i.e., those where theratio is less than about 100:1. In this case the initial arsenic levelwas lower, and even at ratios as low as 11:1 the resulting arsenicconcentration was only 0.050 mg/L. The subexamples of this example alsoshow increased arsenic removal effectiveness when pH is adjusted toabout 7.0 rather than 8.0 as in Example 12.

[0094] Also as in Example 12, this example demonstrates achievingeffective results without introduction of an ionizing step.

EXAMPLE 14 Arsenic in Mining Water

[0095] Example 14 used the same sample water source as Example 12 with adifferent treatment method. The sample was treated for removal ofarsenic in a 3×3 designed experiment with three different residencetimes and three different iron-to-sulfur ratios, including one withoutsulfur. There were also three quality control duplications, for a totalof 12 tests. The experiment was performed in two sets using six mixingjars in each set. A newer batch of Grade B iron was used for thisexperiment and was added at a 200:1 weight ratio of iron-to-arsenic forall conditions. Elemental sulfur was pre-wetted with acetone beforebeing added to the arsenic-contaminated water.

[0096] The six jars were placed in a mixing unit and filled with twoliters each of arsenic-contaminated water with an initial pH of 8.87 forthe first and second sets. No pH adjustments were made. The residencetimes were 15, 30 and 45 minutes and the iron-to-sulfur ratios were 1:0(no elemental sulfur), 2:1 and 4:1. The two sets of six jars werestirred rapidly in the mixing unit at 300 rpm. After the appropriateresidence time, water from each jar was filtered into 250-ml samplebottles and sent to a certified water quality laboratory for analysis ofdissolved arsenic. The laboratory analysis indicated that the conditionswithout sulfur addition (an Fe:S ratio of 1:0) produced the lowestarsenic concentration in this experiment. Sulfur was present in theuntreated water in the form of sulfate at a concentration of 200 mg/L assulfate.

EXAMPLE 14—Jan. 28, 1998

[0097] TIME TEMP As (min) ACTIVITY pH (° F.) LAB NOTES (mg/L) Beginfirst set. −15 Add 2 L of Wharf water to 6 jars. 8.87 68 Yellow tinged0.112 water −1 Pre-wet S with acetone. 0 Increase speed of mixing unitto 300 rpm. 0 Add 0.25 g Fe, Grade B and varying 8.76 dosages of Spre-wetted in acetone. 15 Filter sample jars with 15-min. 8.74 Yellowtinged residence time. water 30 Filter sample jars with 30-min. 8.71Yellow tinged residence time. water Begin second set. −15 Clean jars andadd 2 L of Wharf water 8.78 68 Yellow tinged to 6 jars. water −1 Pre-wetS with acetone. 0 Increase speed of mixing unit to 300 rpm. 0 Add 0.25 gFe, Grade B, and varying 8.75 dosages of S pre-wetted in acetone. 15Filter sample jars with 15-min. 8.73 Yellow tinged residence time. water30 Filter sample jars with 30-min. 8.69 Yellow tinged residence time.water 45 Filter sample jars with 45-min. 8.66 Yellow tinged residencetime. water DISSOLVED ARSENIC CONCENTRATION (mg/L) Residence Fe:S ratioTime (min) 1:0 (No S) 2:1 4:1 15 0.050, 0.049, 0.059 0.061 0.048 300.047 0.058 0.064 45 0.045 0.056 0.063, 0.057

[0098] Hence, this example demonstrates that when sulfur is present inthe untreated water in the form of a sulfate in concentrations as low as200 mg/L, that iron which is not sulfur-modified is effective intraining water.

EXAMPLE 15 Arsenic in Mining Water

[0099] Example 15 used a similar sample water source as Example 12, butwith higher arsenic levels (1.2 mg/L). Example 15 used a similar samplewater source as Example 12, but with higher As levels (1.2 mg/L).Variables for these batch experiments included two types of iron, GradeB and Grade A (MH-100, a coarser iron, particles about twice as large);iron-to-arsenic ratios between 2000:1 and 16,000:1; and iron-to-sulfurratios of 1:1 and 2:1. Since it had previously been determined that thearsenic was in the As⁵⁺ form, the addition of an oxidizing agent such ashydrogen peroxide was deemed unnecessary and therefore was omitted fromthis experiment. No adjustments were made to the initial pH of 8.4.

[0100] Iron and sulfur were mixed in deionized water for 25 minutes inall conditions. The iron, sulfur and contaminated water were then mixedat 300 rpm for 60 minutes. After a settling water from each jar wasfiltered into 250-ml sample bottles and sent to a certified waterquality laboratory for analysis of dissolved arsenic. For allconditions, dissolved arsenic was below the laboratory detection limitof 0.005 mg/L.

EXAMPLE 15—April 1997

[0101] TIME TEMP LAB As (min) ACTIVITY pH (° F.) NOTES (mg/L) Beginfirst set. −25 Pre-wet Fe and S with DI water. 8.4 68 1.2 0 Increasespeed of mixing unit to 300 rpm. 0 First jar: add 4.8 g Fe, Grade A and4.8 g S. 0 Second jar: add 4.8 g Fe, Grade A and 2.4 g S. 0 Third jar:add 38.4 g Fe, Grade A and 38.4 g S. 0 Fourth jar: add 38.4 g Fe, GradeA and 19.2 g S. 60 Let water settle 10 minutes. 7.8 70 Filter samplesfrom each jar. ND Begin second set. −25 Pre-wet Fe and S with DI water.8.4 68 1.2 0 Increase speed of mixing unit to 300 rpm. 0 First jar: add4.8 g Fe, Grade B and 4.8 g S. 0 Second jar: add 4.8 g Fe, Grade B and2.4 g S. 0 Third jar: add 38.4 g Fe, Grade B and 38.4 g S. 0 Fourth jar:add 38.4 g Fe, Grade B and 19.2 g S. 60 Let water settle 10 minutes. 7.870 Filter samples from each jar. ND Fe:As DISSOLVED ARSENIC JAR Fe TYPERATIO Fe:S CONCENTRATION (mg/L) 1 MH 100  2000:1 1:1 ND 2 MH 100  2000:12:1 ND 3 MH 100 16000:1 1:1 ND 4 MH 100 16000:1 2:1 ND 1 Grade B  2000:11:1 ND 2 Grade B  2000:1 2:1 ND 3 Grade B 16000:1 1:1 ND 4 Grade B16000:1 2:1 ND

[0102] As with examples 12-14, this example demonstrates effectiveresults without addition of an oxidizing agent.

EXAMPLE 16 Arsenic in Mining Water

[0103] Example 16 used the same treatment scheme as Example 12 except noadjustments were made to the initial pH of 9.3. The sample water wasalso obtained from the Wharf Mine. Grade B iron and elemental sulfurwere mixed in deionized water at a 1:1 ratio for 30 minutes (Example 12had 2:1 Fe:S ratio). The Fe:As ratios were 960:1, 480:1, 240:1, 96:1,48:1 and 24:1.

[0104] Six jars in a mixing unit were filled with two liters each ofarsenic-containing water. Varying quantities of Grade B iron andelemental sulfur were added to each jar. The jars were stirred rapidlyin a mixing unit at 300 rpm for 24 hours. After 24 hours, the treatedwater from each jar was filtered into 250-ml sample bottles and sent toa certified water quality laboratory for analysis of dissolved arsenic.

[0105] The used iron/sulfur sludge from the experiment was combined intoone sample for Toxicity Characteristic Leaching Procedure (TCLP)analysis. The resulting arsenic concentration was less than thereporting limit of 0.5 mg/L, which meant it easily passed the TCLPcriteria for arsenic of 5 mg/L. Therefore, this sludge would beclassified as non-hazardous waste.

EXAMPLE 16—August 1997

[0106] TIME TEMP LAB As (min) ACTIVITY pH (° F.) NOTES (mg/L) −30Pre-wet Fe and S with DI water 9.3 68 2.5 0 Increase speed of mixingunit to 300 rpm. 0 First jar: add 4.8 g Fe, Grade B and 4.8 g S. 0Second jar: add 2.4 g Fe, Grade B and 2.4 g S. 0 Third jar: add 1.2 gFe, Grade B and 1.2 g S. 0 Fourth jar: add 0.48 g Fe, Grade B and 0.48 gS. 0 Fifth jar: add 0.24 g Fe, Grade B and 0.24 g S. 0 Sixth jar: add0.12 g Fe, Grade B and 0.12 g S. 1440 Filter samples from each jar.DISSOLVED ARSENIC JAR Fe:As RATIO CONCENTRATION (mg/L) 1 960 ND 2 480 ND3 240 0.005 4 96 0.680 5 48 1.420 6 24 1.430

[0107] This example also demonstrates that although less effective, theuse of lower iron concentration can still yield significant and valuablereductions of arsenic levels. Furthermore, this example demonstrateseffective removal of arsenic at pH levels as high as 9.3. This asignificantly wide effective pH range, and these results consideredalong with Examples 1-11 tend to indicate that a pH range of about 3.5to about 10.0 is effective.

EXAMPLE 17 Arsenic in Mining and Drinking Water

[0108] This example used the same sample water as Example 12, but thewater was “spiked” with 1 mg/L arsenic adding 94 ml of arsenic trioxideto 25 gallons of Wharf mire water. The sample water was treated forremoval of arsenic by continuous flow through a 16-inch packed-bedcolumn (composed of 15% wt. Grade B iron, 0.15% wt. elemental sulfur and84.85% wt. silicia sand). The middle 10 inches of the column were packedwith an iron/sulfur/sand mixture. The top and bottom 3 inches of thecolumn were packed with pure silicia sand. The inside diameter of thecolumn was {fraction (9/16)} of an inch. The porosity of the silica sandwas 0.4. The pH of the untreated water was 7.78.

[0109] Untreated water was pumped into the column at a flow rate of 1.5ml/min, generating a packed-bed residence time of approximately 15minutes. A beaker was placed at the end of the column for effluentcollection. Influent and effluent pH values were measured weekly.Initially, samples were collected daily and sent to a certified waterquality laboratory for analysis of dissolved and total arsenic and iron.Since no iron was detected after the first week, the remaining sampleswere only analyzed for total arsenic and collected every other day.After about two weeks of operation, the “spiked” Wharf water wasreplaced with “spiked” tap water which also contained 1 mg/L arsenic.All arsenic was present in the reduced form, As³⁺, but an oxidizingagent was not added.

EXAMPLE 17—February-March 1998

[0110] TIME TEMP As (day) ACTIVITY pH (° F.) LAB NOTES (mg/L) 0 Make upcolumn, 3 in. sand on either end, 10 in. sand/Fe/S mix in middle. 0 Setpump flow at 1/5 ml/min. 0 Measure pH influent. 7.78 68 0 Take influentsample, filtered. 7.78 68 0.912 0 Turn on pumps. 1 Take influent sample,filtered and 7.78 0.820 unfiltered. 1 Take effluent samples, filteredand 8.21 Yellow tinged 0.019, unfiltered, water 0.032 2 Take effluentsamples, filtered. 8.16 Yellow tinged ND, water ND 6 Take effluentsample, unfiltered. Yellow tinged 0.027 water, Fe beginning to oxidize 7Take influent sample, filtered. 0.330 7 Take effluent sample,unfiltered. Yellow tinged 0.033 water 8 Take effluent sample,unfiltered. 8.40 Yellow tinged 0.046 water 9 Take influent sample,unfiltered. 0.272 9 Take effluent sample, unfiltered. 8.45 Yellow tinged0.043 water 12 Take influent sample, unfiltered. 8.20 0.156 12 Takeeffluent sample, unfiltered. 8.45 Yellow tinged 0.057 water 13 Make upnew mixture of “spiked” tap water. 13 Take influent sample, unfiltered.6.85 0.195 14 Take effluent sample, unfiltered. 7.02 Yellow tinged 0.076water 16 Take effluent sample, unfiltered. 7.02 Yellow tinged 0.038water

[0111] The influent concentration of untreated water decreased over timebut remained greater than 0.150 mg/L. Effluent arsenic removal wasobtained in the column, as effluent concentrations ranged from 0.076mg/L to below the detection limit of 0.005 mg/L. An oxidizing agent wasnot added, and this was the only experiment treating water with arsenicin its reduced state, As³⁺. This example demonstrates that the treatmentof water in a reactor column packed with an inert medium, in this casesand, may afford increased permeability and yield effective results in acontinuous flow operation over extended periods of time. In all ofExamples 12 to 17, no oxidizing step was used. The examples show veryeffective arsenic removal without the oxidizing step, for both thearsenate and arsenite forms of arsenic in water.

[0112] Additional tests were made to test certain parameters of theprocess. These tests are reflected in Examples 12 to 17.

EXAMPLE 18—November 2000 Start

[0113] A field pilot test for removal of arsenic was conducted for threemonths using specially-programmed off-the-shelf pressure filtrationequipment, specifically, water-softening vessels, valves and pumps.Water was taken from a ground water well producing domestic water for apublic water system in the Central Valley of California. This water wastreated in a pressure filter and wasted to a designated disposal area.Approximately 170,000 gallons was put through a 12-inch diameterpressure column with a 24-inch SMI bed depth at a flow rate of 2.8gallons per minute. Empty Bed Contact Time was approximately 4 minutes.The influent concentration was 0.018mg/L As and the effluentconcentration was <0.002 mg/L throughout the test. The test was stoppedprior to breakthrough.

[0114] Additional field pilot testing has been undertaken for nitrateand arsenic removal from drinking water. Field testing for removal ofchrome VI has also been performed, results being shown on the two tablesbelow. These tests prove SMI effectiveness under field conditions fordirect scale-up to production equipment to meet urgent water treatmentneeds.

[0115] Numerous laboratory column tests were conducted to test theeffectiveness of SMI for removal of contaminants from industrialwastewater and domestic water supplies. Some of these tests aresummarized in two tables which follow: “Summary of SMI LaboratoryTesting” and “Laboratory Development Studies of SMI.”

[0116] Prima Environmental, an applied sciences and technologylaboratory, performed the tests summarized in the tables. The testcolumn was configured as shown in the accompanying drawing, FIG. 4.

[0117] Typically, 50 grams of SMI Mix 1,3, 4, or 5 was placed between 10g of clean 90-mesh silica sand. One flow rate used for the columns was2.3 to 2.5 mL/min. Contact time at that rate of flow was 5 minutes.Other flow rates were used in some of the tests to obtain differingcontact times.

[0118] SMI mixes 1-5 were prepared as follows:

[0119] All mixes were prepared in a laboratory, using sponge iron(designated No. 423A, Hoeganaes) and sulfur, 200 grams iron and 12 gramssulfur, a ratio of about 16.7:1 or 17:1. The iron and sulfur were mixedwith a sufficient quantity of deionized water to keep the mixturecontinuously moist, and to start the reaction, and sufficient deionizedwater to keep the reaction going continuously, with continuous mixing.Water was sometimes added after start of the reaction. Mixing wasperformed by hand with a paddle mixer. In addition, heat was added tothe vessel, so that the water and the reagents were heated to anelevated temperature, which varied from mix to mix as noted in the tablebelow. Approximately 10 to 50 ml of water were used in mixes.

[0120] Completion of the reaction was indicated by the cessation of gas,which is given off during the reaction, and the color of the reactedSMI, which is very black. Mix Number Temperature Duration of Mixing 1 80° F. 10 minutes 2 100° F. 20 minutes 3 120° F. 20 minutes 4 140° F.30 minutes 5 140° F. 30 minutes

[0121] Following the completion of the reaction in each mix, the mix wascooled, during which the SMI essentially dried. The SMI was then sealedin packaging to prevent oxidation.

[0122] The various mixes were prepared under the conditions stated aboveto determine the efficacy of using heat and water to produce afully-reacted SMI. Generally the results showed that the reactionproducing SMI went to completion more quickly using heat to elevate thetemperature as compared with reactions started at room temperature, andthat the efficacy of the resulting SMI was not adversely affected.

[0123] The SMI mixes were used by placing each mix into a separate smallreactor column, essentially as shown in FIG. 4. SUMMARY OF SMILABORATORY TESTING Reaction Conditions Date Purpose SMI Other ResultsSummary Dec. 11, 1998 Compare ability of various SMI types MH 100, GradeB, — All compounds at least partially removed to remove TCE, CF,nitrate, sulfate Castwell iron + sulfur Dec. 16, 1998 Effect of SMI onnitrate, use of 1824 Grade B iron + sulfur — Nitrate > 90% removed withcontact time of gum as suspending agent 12 minutes Dec. 16, 1998Perchlorate removed iron + sulfur — No perchlorate removed; conditionsnot optimized Feb. 24, 2000 Batch test to compare SMI S4 & S6 S4 & 56 —S6 slightly better than S4; As loading ranged for As removal from0.56-4.5 mg/g SMI depending upon initial As conc. Apr. 05, 2000 CompareMix 1, 3, & 4 for As removal Mix 1, 3, & 4 25 ppm As As < 0.005 mg/L at2 hours; 3.6-7.9 mg/L at 44 hours; est. As loading 2-3 mg/g SMI,depending upon assumptions Apr. 01, 2000 Column test for Mix 4, Asremoval Mix 4 2.5 ppm As As < 0.005 mg/L for 10 days; loading about 3 mgAs/g SMI May 01, 2000 Mix 4 tap water, As removal Mix 4 2.5 ppm As As <0.005 mg/L for < 5 days; complete clogging by 7 days May 01, 2000 Mix 5deionized water, As removal Mix 5 2.5 ppm As As < 0.005 mg/L for 8-11days; stirred SMI when effluent was 0.050 mg/L, but this did not reduceAs concentration Jun. 06, 2000 Removal of nitrate Mix 5 11 ppm Nitrate32% nitrate removal with 5 min contact time; can probably improveremoval if increase contact time

[0124] Laboratory Development Studies of SMI Water EBCT InfluentEffluent % Re- Capacity Contaminant Source min mg/L mg/L moval mg/g SMIAs(III)/ DI 10 2.7 <0.005 100 2 As(V) Total As IWW 17 17 <0.01 100 3Total As GW 7 11 <0.005 100 n.m. 23 11 <0.005 100 Nitrate GW 7 32 30 6n.m. 23 32 19 41 Nitrate DI 27 53 35 34 n.m. 31 53 13 75 Cr(VI) DI 6 0.9<0.02 >98 n.m. Copper DI 5 10 <0.1 >99 >2   Trichloro- GW 28 0.008<0.001 >87 n.m. ethene

[0125] An improved process for producing SMI minimizes water content information of the pre-mix, and takes advantage of the exothermicreaction, utilizing heat to reduce reaction time.

[0126] In some of the examples above the pre-mix preparation involved asignificant amount of water, with the reagents placed into water to forma wet slurry. The water fraction of the mix was very much larger thanthe sulfur and iron fraction. A variation, used in Example 18 above,speeds reaction time and reduces the bulk of the resulting SMI product,by virtual elimination of water. By this method only enough water ispresent to moisten the iron and the sulfur, the moisture not filing allthe interstices among the iron and sulfur particles in the mix. The SMIreaction is exothermic, and with minimal water present, this exothermicreaction significantly heats the mix, speeding the reaction time. Theelevated temperature may create a different chemical result and chemicalbonding properties, since temperatures above about 100° F. usuallyresult in sulfur being present in the “thio” form.

[0127] The reaction can be allowed to heat up to about 140° to 180° F.,but should not be allowed to go significantly higher because of the riskof explosion. The temperature can accelerate to the extent that thehigher temperatures continue to speed the reaction time, causing evenmore heat to be released, rapidly drying the water into steam andcausing an explosion. Cooling can be used, such as cooling coils aroundthe reaction vessel, to control the temperature if needed. Anotherimportant aspect of the process is to blend the mixture occasionally orcontinuously, to distribute the heat generated in the process andminimize hot spots. This can be done in commercial quantities using arotating drum, for example.

[0128] In a preferred procedure the initial moisture is minimized, onlysufficient to moisten the iron and sulfur mixture, and as the heat ofreaction raises the temperature, further water can be added if and asneeded. The mixture can be allowed to begin on its own, or, to hastenthe start of the reaction, heat can be initially added, to raise theinitial temperature to between about 80° F. and 140° F. The reactionwill then continue, with proper blending, to completion unless the watercompletely dries, and the reaction can then be continued by addition ofwater. In this way, the water content and the addition of water cancontrol the speed of the reaction.

[0129] This method results in a savings in cost and time, in that thereaction time is lessened and the pre-mix dries from its heat ofreaction, no separate drying process being necessary. This dry pre-mixis less bulky and is easier to pack, ship and store.

[0130] Thus, in an implementation of the above described method,elemental powdered sponge iron is mixed with dry powdered sulfur andwater in a container. The water quantity is only sufficient to keep theresulting mixture moist and to stimulate a reaction, not filling allinterstices in the iron and sulfur particles. Heat is added to initiatethe reaction, if desired, although this is not necessary. The reactionis exothermic and builds up heat in the mixture, as noted above. Themethod allows the heat of the reaction to elevate the temperature of themixture, speeding the reaction. The mixture is occasionally orcontinuously blended, to distribute heat and prevent hot spots in themixture. Also, the mixture is controlled to prevent overheating;blending assist in this control, but cooling can be used if necessary,and limitation of water content, with addition of water as needed, canalso control the speed and heat of reaction.

[0131] Once the reaction is complete, the resulting SMI mix isrelatively dry. This SMI product is cooled (which can be by allowing itto cool to near ambient) and packed in a sealed container to preventoxidation, then shipped and/or stored, or put into a contact bed, in theform of a particulate bed through which water can be passed. Then, inuse of the contact bed, water containing dissolved contaminants ispassed through the bed. Contact is maintained between the water and theparticulate sulfur-modified iron in the contact bed sufficient to effectremoval of at least a part of the contaminants in the water, byadsorption and absorption onto the sulfur-activated iron particles.

[0132] The above-described preferred embodiments are intended toillustrate the principles of the invention, but not to limit its scope.Other embodiments and variations to these preferred embodiments will beapparent to those skilled in the art and may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

I claim:
 1. A method for removing contaminants from drinking water,comprising: preparing a sulfur-modified iron pre-mix by the steps ofadding elemental powdered sponge iron, dry powdered sulfur and water toa container, the water quantity being sufficient to keep the resultingmixture continuously moist and to stimulate a reaction; elevating thetemperature of the mixture to between about 80° F. and 140° F.;agitating the mixture until completion of a reaction; and cooling themixture to form a concentrated sulfur-modified iron pre-mix includingsulfur-activated sponge iron particles; forming a contact bed of thesulfur-modified iron pre-mix, in the form of a particulate bed throughwhich water can be passed; passing through the contact bed watercontaining dissolved contaminants; and maintaining contact between thewater and the particulate sulfur-modified iron in the contact bedsufficient to effect removal of at least a part of the contaminants inthe water, by adsorption and absorption onto said sulfur-activated ironparticles, the method being conducted without an oxidizing step.
 2. Themethod of claim 1, wherein the iron and sulfur are added in a quantityat a weight ratio of about 17:1.
 3. The method of claim 1, wherein thewater is passed through the contact bed in an upflow direction.
 4. Themethod of claim 1, wherein the water is passed through the contact bedunder pressure.
 5. The method of claim 1, further including removingspent sulfur-modified iron from the contact bed when the sulfur-modifiediron has essentially lost its effectiveness in removing contaminantsfrom water, then using the spent sulfur-modified iron as feed stock toan iron or steel producing facility.
 6. The method of claim 1, includingdrying the sulfur-modified iron mixture after completion of thereaction.
 7. A method for preparing a sulfur-modified iron pre-mix,comprising: mixing elemental powdered sponge iron, dry powdered sulfurand water in a container, the water quantity being only sufficient tokeep the resulting mixture moist and to stimulate a reaction, notfilling all interstices in the iron and sulfur and causing an exothermicreaction, allowing the heat of the reaction to elevate the temperatureof the mixture, blending the mixture at least occasionally during thereaction, until completion of the reaction, and adding water if and asneeded to maintain the reaction, and cooling the mixture to form aconcentrated sulfur-modified iron pre-mix including sulfur-activatedsponge iron particles.
 8. The method of claim 7, further includingcontrolling the temperature of the reaction by cooling the mixture inthe container during the reaction.
 9. The method of claim 7, furtherincluding initially heating the iron, sulfur and water mixture in thecontainer to start the reaction, then allowing the exothermic nature ofthe reaction to further elevate the temperature of the mixture.
 10. Themethod of claim 9, wherein the temperature to which the mixture isinitially heated is above about 80° F.
 11. The method of claim 7,wherein the iron and sulfur are added in a quantity at a weight ratio ofabout 17:1.
 12. A method for removing contaminants from drinking waterusing the sulfur-modified iron pre-mix according to claim 7, comprising:forming a contact bed of the sulfur-modified iron pre-mix, in the formof a particulate bed through which water can be passed; passing throughthe contact bed water containing dissolved contaminants; and maintainingcontact between the water and the particulate sulfur-modified iron inthe contact bed sufficient to effect removal of at least a part of thecontaminants in the water, by adsorption and absorption onto saidsulfur-activated iron particles.
 13. The method of claim 12, wherein thewater is passed through the contact bed in an upflow direction.
 14. Themethod of claim 12, wherein the water is passed through the contact bedunder pressure.
 15. The method of claim 12, further including removingspent sulfur-modified iron from the contact bed when the sulfur-modifiediron has essentially lost its effectiveness in removing contaminantsfrom water, then using the spent sulfur-modified iron as feed stock toan iron or steel producing facility.